Optical waveguide splitter on a waveguide substrate for attenuating a light source

ABSTRACT

An optical apparatus comprises: source, primary, and secondary waveguides formed in waveguide layers on a substrate; a light source; and an optical waveguide tap. The light source launches a source optical signal along the source waveguide. The tap divides the source optical signal into a primary optical signal in the primary waveguide and a secondary optical signal in the secondary waveguide. The secondary optical signal emerges from the secondary waveguide to exit the waveguide layers at the substrate edge or to propagate within the waveguide layers as a stray optical signal without confinement by any waveguide. The stray optical signal propagates thusly unconfined into the open mouth of an optical trap that comprises one or more lateral surfaces formed in the waveguide layers and an opaque coating on the lateral surfaces, and comprises a spiral region of the optical waveguide layers with an open mouth and closed end.

RELATED APPLICATIONS

This application is a continuation of U.S. non-provisional applicationSer. No. 13/662,418 filed Oct. 27, 2012 in the names of Peter C. Sercel,Toshiaki Sonehara, and Rolf A. Wyss, which in turn claims benefit ofU.S. provisional App. No. 61/553,133 filed Oct. 28, 2011 in the names ofPeter C. Sercel, Toshiaki Sonehara, and Rolf A. Wyss. Both of saidapplications are hereby incorporated by reference as if fully set forthherein.

BACKGROUND

The field of the present disclosure relates to optical waveguides. Inparticular, apparatus and methods are described herein that employ awaveguide tap or splitter on a waveguide substrate for attenuating theoutput of a light source.

A common configuration for an optoelectronic device includes a substrateon which are formed one or more optical waveguides, and at least onelight source positioned (perhaps mounted on the substrate) to launch atleast a portion of its optical output signal into an optical waveguideon the substrate. The optical signal thus launched propagates along theoptical waveguide in a corresponding guided optical mode that issubstantially confined in two transverse dimensions.

In many instances, a standard light source (e.g., a laser diode) isincorporated into the assembled optoelectronic device; the standardlight source might be manufactured by the same manufacturer thatassembles the optoelectronic device, or might be obtained from adifferent manufacturer of merchant or OEM light sources. In some cases,the optimum operating output power of the standard laser diode is largerthan the maximum optical signal power permitted or desired in or fromthe optoelectronic device (e.g., to comply with an established industrystandard). Operating the laser diode at reduced output power, byreducing the drive current to a level that is not sufficiently above itslasing threshold current, can reduce the maximum speed or frequency atwhich the laser output can be modulated, or can reduce the risetime orintroduce timing jitter at the leading edge of a modulated waveform.Operating at reduced current might also introduce spectral changes,power fluctuations, or other undesirable fluctuations or instabilities,or might require more precise control of DC laser bias current ormodulation current amplitude to maintain a fixed extinction ratio.

Redesigning the laser diode to run optimally at lower output power, orre-sourcing a merchant laser diode to replace it with a different onethat operates at lower output power, can incur significant costs, risks,and penalties, both technical and commercial. A more straightforwardapproach might include intentional introduction of an optical losselement into the optical waveguide, to reduce the power level of thepropagating optical signal after it leaves the laser diode. In that waythe standard laser diode or other light source can be operated at itsoptimal power level, but only a desired fraction of that output powerpropagates beyond the optical loss element.

SUMMARY

An optical apparatus comprises: a waveguide substrate; one or moreoptical waveguide layers on the substrate; source, primary, andsecondary waveguides formed in the waveguide layers; a light source; andan optical waveguide tap. The apparatus can further comprise one or morelight traps. Each of the waveguides is arranged to substantially confinein two transverse dimensions a corresponding guided optical mode. Thelight source emits an optical signal and is arranged to launch a portionof the optical signal to propagate along the source waveguide as asource optical signal in the corresponding guided optical mode. Theoptical waveguide tap is formed in one or more of the optical waveguidelayers and is arranged to direct a primary fraction of the sourceoptical signal to propagate along the primary waveguide as a primaryoptical signal and to direct a secondary fraction of the source opticalsignal to propagate along the secondary waveguide as a secondary opticalsignal. Each light trap is formed in the optical waveguide layers andcomprises one or more lateral surfaces of the optical waveguide layersand a substantially opaque coating on the lateral surfaces.

The secondary waveguide can be arranged so that the secondary opticalsignal propagates to an end of the secondary waveguide, propagates to anedge of the waveguide substrate, and emerges from the optical waveguidelayers.

The lateral surfaces of each light trap can be arranged to define acorresponding spiral region of the optical waveguide layers; the regionincludes an open mouth and closed end of the light trap. The secondarywaveguide can be arranged so that the secondary optical signalpropagates to an end of the secondary waveguide and emerges from thesecondary waveguide to propagate as a stray optical signal in one ormore of the optical waveguide layers without confinement by any of theoptical waveguides in the corresponding guided optical modes. Thesecondary waveguide and the light trap can be arranged on the waveguidesubstrate so that the stray optical signal propagates into the openmouth of the optical trap without confinement by any of the opticalwaveguides in the corresponding guided optical modes.

Objects and advantages pertaining to attenuating an optical signalpropagating in a waveguide using a waveguide tap or a light trap maybecome apparent upon referring to the exemplary embodiments illustratedin the drawings and disclosed in the following written description orappended claims.

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic plan view of an exemplary arrangement of a lightsource, waveguide, and waveguide tap on a waveguide substrate. FIG. 1Bis a schematic plan view of another exemplary arrangement of a lightsource, waveguide, and waveguide tap on a waveguide substrate.

FIG. 2A is a schematic plan view of a light source, waveguide, andexemplary light-trapping structure on a waveguide substrate; FIG. 2B isa schematic plan view of the light source, waveguide, and exemplarylight-trapping structure of FIG. 2A showing paths of guided and strayoptical signals.

FIGS. 3A, 4A, and 5A are schematic cross-sectional views of variousexemplary lateral surfaces of the optical waveguide layers andsubstantially opaque coatings formed near an optical waveguide.

FIGS. 3B, 4B, and 5B are schematic cross-sectional views of othervarious exemplary lateral surfaces of the optical waveguide layers andsubstantially opaque coatings formed away from any optical waveguide.

FIGS. 6A, 7A, and 8A are schematic longitudinal sectional views of endfaces of various exemplary optical waveguides and substantially opaquecoatings formed on the end faces.

FIGS. 6B, 7B, and 8B are schematic longitudinal sectional views of endfaces of other various exemplary optical waveguides and substantiallyopaque coatings formed on the end faces.

FIG. 9A is a schematic plan view of an exemplary arrangement of a lightsource, waveguide, waveguide tap, and monitor tap on a waveguidesubstrate. FIG. 9B is a schematic plan view of another exemplaryarrangement of a light source, waveguide, waveguide tap, and monitor tapon a waveguide substrate.

The embodiments depicted in this disclosure are shown onlyschematically, and that not all features may be shown in full detail orin proper proportion. Certain features or structures may be exaggeratedrelative to others for clarity. The drawings should not be regarded asbeing to scale. The embodiments shown are exemplary only, and should notbe construed as limiting the scope of the written description orappended claims.

DETAILED DESCRIPTION OF EMBODIMENTS

As noted above, it may be desirable in some optoelectronic devices (i)to employ a light source that, when operated in its optimal output powerrange, delivers more optical signal power than is permitted or desiredin or from the optoelectronic device, and (ii) to intentionallyintroduce loss into an optical waveguide on a waveguide substrate so asto reduce the optical signal power to a desired or permitted level whilestill operating the light source in its optimal range. In the exemplaryembodiments of the present disclosure, an optical loss element in theoptical waveguide carrying the optical signal (referred to herein as thesource waveguide) comprises a waveguide tap formed in waveguide layerson the waveguide substrate. The waveguide tap (equivalently, waveguidesplitter) is arranged to direct a desired fraction of the optical signalpower from the source waveguide into a secondary optical waveguide. Thatsecondary waveguide terminates, allowing the diverted portion of theoptical signal to freely propagate within the waveguide substrate,within layers on the waveguide substrate, or out of the waveguidesubstrate. The fraction of the optical signal directed into thesecondary waveguide shall be referred to herein as the secondaryfraction (equivalently, the dumped fraction); the remaining fraction isdirected into a primary waveguide and shall be referred to herein as theprimary fraction. The primary fraction of the optical signal representsthe desired optical output of the optoelectronic device.

In any embodiment of an optoelectronic device according to the presentdisclosure, any suitable waveguide tap or splitter can be employed, andcan be arranged to divide between the primary and secondary waveguidesany desired fractions of the optical signal power propagating along thesource waveguide. Examples are disclosed in, e.g., co-owned U.S. Pat.No. 7,330,619, U.S. Pat. No. 7,813,604, and U.S. Pat. No. 7,945,132,each of which is incorporated by reference as if fully set forth herein.Other examples are disclosed in, e.g.:

-   -   U.S. Pat. No. 4,750,799 entitled “Hybrid optical integrated        circuit”;    -   U.S. Pat. No. 5,133,029 entitled “Adiabatic polarization        splitter”;    -   U.S. Pat. No. 5,375,178 entitled “Integrated optical        polarization manipulating device”;    -   U.S. Pat. No. 5,418,867 entitled “Integrated optical device for        manipulating the polarization of optical signals”;    -   U.S. Pat. No. 6,885,795 entitled “Waveguide tap monitor”;    -   U.S. Pat. No. 7,340,114 entitled “Optical waveguide device and        optical modulator”;    -   Hu et al, “A Low-Loss and Compact Waveguide Y-Branch Using        Refractive-Index Tapering”, IEEE Photonics Technology Letters,        vol. 9, No. 2, pp. 203-205 (February 1997);    -   Rangaraj et al, “Low Loss Integrated Optical Y-Branch”, Journal        of Lightwave Technology, vol. 7, No. 5, pp. 753-758 (May 1989);        and    -   Shirafuji et al, “Transmission Characteristics of Optical        Asymmetric Y Junction with a Gap Region”, Journal of Lightwave        Technology, vol. 9, No. 4, pp. 426-429 (April 1991),        each of which is incorporated by reference as if fully set forth        herein. In some examples the core of the primary or secondary        waveguide is a continuous extension of the core of the source        waveguide; in some examples the core of the primary or secondary        waveguide is discrete from but optically coupled to the core of        the source waveguide. Any suitable waveguide tap or splitter        arrangement, including those examples cited above, shall fall        within the scope of the present disclosure or appended claims.

The optical waveguides (source, primary, secondary, and otherwaveguides, if present, formed on the waveguide substrate as part of theoptoelectronic device) typically are formed in one or more layers ofsuitable core or cladding materials grown, deposited, or otherwiseformed on the substrate; those layers can be referred to collectively asoptical waveguide layers. The waveguide substrate acts as a structuralsupport for the optical waveguide layers. While the waveguides areformed, strictly speaking, in the optical waveguide layers, they mayalso be referred to herein (equivalently if somewhat less precisely) asbeing formed on the waveguide substrate. The light source is mounted onthe waveguide substrate, directly or on one or more of the opticalwaveguide layers, and can be configured and positioned in any suitableway for launching at least a portion of its optical output signal intoone of the waveguides formed in the optical waveguide layers. Spatiallyselective processing of one or more of the optical waveguide layers (bydeposition, removal, or alteration of material) defines the opticalwaveguides; those processed layers (or processed regions of thoselayers) often act as waveguide cores having a refractive index somewhathigher than surrounding layers, which act as waveguide cladding. Atypical waveguide substrate can include regions having only claddinglayers and other regions having one or more core layers in addition tocladding layers. In some examples of waveguides formed on substrates(e.g., co-owned U.S. Pat. Nos. 6,975,798; 7,136,564; 7,164,838;7,184,643; 7,373,067; 7,394,954; 7,397,995; or 7,646,957, or co-ownedPub. No. 2010/0092144, each of which is incorporated by reference as iffully set forth herein), distinct regions can have differing numbers ofcore or cladding layers present, with the waveguide typically beingdefined by those regions where certain sets of core layers are present.Any suitable core/cladding configurations can be employed within thescope of the present disclosure or appended claims.

Once propagating along the secondary waveguide, the secondary fractionof the optical signal is discarded (i.e., the dumped fraction isdumped). However, the dumped secondary fraction must be suitably managedso as to reduce or eliminate potential degradation of the performance ofthe optoelectronic device (e.g., via optical feedback to the lightsource or optical cross-talk). A portion of the dumped fraction of theoptical signal, propagating as a stray optical signal in the opticalwaveguide layers but not guided by a waveguide core, can cause a varietyof problems in the optoelectronic device. For example, a stray opticalsignal that propagates back to the light source can cause instabilitiesor fluctuations through unwanted optical feedback. In another example,if a monitor photodetector is used for electronic feedback control ofthe light source, a stray optical signal that reaches the monitorphotodetector can disrupt that feedback control. In another example, ifthe optoelectronic device is a bidirectional device (e.g., abidirectional transceiver comprising both a transmitting light sourceand a receiving photodetector), then a stray optical signal that reachesthe receiving photodetector can interfere with reception of a receivedoptical signal (a problem known as optical cross-talk and oftenquantified as a so-called “cross-talk penalty”). Those and otherproblems can be reduced, eliminated, or mitigated by limiting orcontaining the propagation in the waveguide layers of the dumpedsecondary fraction of the optical signal as a stray optical signal.

Control of propagation in the waveguide layers of the dumped secondaryfraction as a stray optical signal can be achieved by routing thesecondary waveguide toward an edge of the waveguide substrate, asschematically illustrated in the exemplary arrangements of FIGS. 1A and1B. An optical source waveguide 40 of any suitable type or configurationis formed in optical waveguide layers 20 on a waveguide substrate 10.The optical waveguide layers 20 and the waveguide substrate 10 cancomprise any of myriad suitable materials while remaining within thescope of the present disclosure or appended claims. In a commonimplementation, substrate 10 comprises silicon, and the waveguide layers20 can include one or more of silica, doped silica, silicon nitride, orsilicon oxynitride. Some suitable examples of optical waveguides aredisclosed in co-owned patents and published applications cited above.Other waveguide layer compositions and arrangements can be employed(e.g.: one or more inorganic, doped or undoped, dielectric, core orcladding material; one or more polymer or organic, doped or undoped,dielectric, core or cladding material; silicon or other doped or undopedinorganic semiconductor core material(s) in silica or other doped orundoped inorganic dielectric cladding material(s); doped or undoped,polymer or organic, semiconductor core material(s) in doped or undoped,polymer or organic, dielectric cladding material(s); or combinations orfunctional equivalents thereof).

A light source 90 can be positioned on substrate 10 or on one or more ofthe waveguide layers 20, and is positioned to launch an optical signal30 to propagate along optical source waveguide 40 as a guided opticalmode substantially confined by the waveguide 40 in two transversedimensions. Alternatively, the light source 90 can be located elsewhere(i.e., not mounted on the substrate 10) and the optical signal 30 can beconveyed by any suitable optical arrangement (e.g., using a lens) to belaunched to propagate along optical source waveguide 40. The lightsource 90 can comprise any source of optical signal 30, such a laserdiode or light-emitting diode; such a light source often exhibitsreduced modulation speed or undesirable shifts, fluctuations, orinstabilities of performance characteristics when operated below itsoptimal output power range. Laser diodes can be particularly susceptibleto such undesirable behaviors when operated at lower-than-optimal outputpower or too near their lasing threshold currents.

A waveguide tap 42 is formed in the waveguide layers 20 and couples thesource waveguide 40 with a primary optical waveguide 44 and a secondaryoptical waveguide 46, which are also formed in the waveguide layers 20.The waveguide tap 42 is arranged to divide the optical signal 30 guidedby the source waveguide 40 into a primary optical signal 34 guided bythe primary waveguide 44 and secondary optical signal 36 guided by thesecondary waveguide 46. The tap 42 is arranged so that the primaryoptical signal 34 falls within a desired output power range for theoptoelectronic device when the light source 90 operates within itsoptimal output power range. The dumped secondary optical signal 36 isoften between about 50% and about 99% of the optical signal 30,typically between about 70% and about 95%, and preferably between about80% and about 90%; other so-called tap ratios can be employed as neededor desired in a particular circumstance. Any suitable type orarrangement of waveguide tap can be employed. In one example,mode-interference coupling can be employed (e.g., as in U.S. Pat. No.7,330,619 noted above) to divide the optical signal 30 into primary andsecondary optical signals 34 and 36. In such an example, a desired tapratio can be implemented by forming the waveguide tap 42 with, e.g., asuitable gap between the waveguide tap segments in a coupling region, asuitable length of the coupling region, and so on.

In FIG. 1A, the secondary waveguide 46 is routed to an edge of thewaveguide substrate 10 and waveguide layers 20, and the dumped secondaryfraction 36 of the optical signal propagates to the end of the secondarywaveguide 46 and then propagates into the surroundings as an unconfinedstray optical signal 38. The core of the waveguide 36 can be terminatedby the edge of the waveguide layers 20, or the core can terminate atsome desired distance from the edge (not shown). Terminating the core ofthe secondary waveguide 46 at the edge can result in less of the opticalsignal 36 escaping into the waveguide layers 20; terminating the corebefore it reaches the edged permits the dumped optical signal 36 todiverge before reaching the edge, thereby reducing the power density andthe likelihood of damage or undesirable localized heating of thewaveguide layers 20 or the substrate 10 (if those are a concern).

An index matching medium can be employed to reduce internal reflectionof the secondary optical signal 36 by the edge of the waveguide layers20. Such an internally reflected optical signal can propagate in theoptical waveguide layers 20 without confinement by any waveguide, whichcan be undesirable (see below). Instead or in addition, the waveguide 46can be arranged so that the secondary optical signal exits the waveguidelayers 20 at Brewster's angle to reduce the amount of that signalreflected back into the waveguide layers 20. If an index matching mediumis employed, it can include an optical absorber that absorbs the strayoptical signal 38 once it exits the waveguide layers and enters thesurrounding medium. By conveying the dumped secondary optical signal 36out of the waveguide layers 20, the likelihood of degradation by thatsignal of the operation of the optoelectronic device (e.g., via opticalfeedback to the light source or optical cross-talk) can be reduced.

Another exemplary arrangement of an optoelectronic device is illustratedschematically in FIG. 1B, in which the dumped secondary optical signal36 exits the secondary waveguide 36 and propagates as a stray opticalsignal 38 in the optical waveguide layers 20 without confinement by anywaveguide. A light collector 110 a is formed in the waveguide layers 20on the waveguide substrate 10. The structure of the light collector 110a is described below and illustrated schematically in the sectionalviews of FIGS. 6A/6B, 7A/7B, and 8A/8B. In this example the lightcollector 110 a is arranged to reflect the stray optical signal 38 topropagate toward an edge of the waveguide layers 20 (without confinementby any of the optical waveguides in the corresponding guided opticalmodes) and into the surrounding medium. The surrounding medium can beindex matched, optically absorbing, or both, as described above; thewaveguide 46 and light collector 110 a can be arranged so that theoptical signal 38 exits the waveguide layers 20 at Brewster's angle, asdescribed above.

In some optoelectronic devices, the arrangements of FIG. 1A or 1B mightbe sufficient for reducing to an operationally acceptable levelunconfined propagation of the stray optical signal 38 in the waveguidelayers 20. In other instances, more stringent requirements mightnecessitate additional measures to reduce further such unconfinedpropagation of the stray optical signal 38 in the waveguide layers 20.Further reduction of propagation in the waveguide layers 20 of thedumped secondary fraction 36 as an unconfined stray optical signal 38can be achieved by providing one or more additional light-collecting orlight-trapping structures formed in the waveguide layers 20 that arearranged to collect or trap the dumped secondary fraction of the opticalsignal that emerges from an end of the secondary waveguide. Someexamples of such structures are disclosed in one or more of thefollowing co-owned applications:

-   -   U.S. provisional App. No. 61/358,877 filed Jun. 25, 2010        entitled “Light-trapping structure on a waveguide substrate”;    -   U.S. provisional App. No. 61/380,310 filed Sep. 6, 2010 entitled        “Multi-function encapsulation for a multi-channel optoelectronic        device”;    -   U.S. non-provisional application Ser. No. 13/096,648 filed Apr.        28, 2011 entitled “Cross-talk reduction in a bidirectional        optoelectronic device”;    -   U.S. non-provisional application Ser. No. 13/168,936 filed Jun.        25, 2011 entitled “Cross-talk reduction in a bidirectional        optoelectronic device”; and    -   U.S. non-provisional application Ser. No. 13/225,723 filed Sep.        6, 2011 entitled “Cross-talk reduction in a bidirectional        optoelectronic device.”        Each of said applications is incorporated by reference as if        fully set forth herein. Other examples of light-trapping        structures (not all of which are formed on waveguide substrates)        are disclosed in:    -   U.S. Pat. No. 6,418,246 entitled “Lateral trenching for cross        coupling suppression in integrated optical chips” issued Jul. 9,        2002 to Gampp;    -   U.S. Pat. No. 6,959,138 entitled “Planar optical waveguide”        issued Oct. 25, 2005 to Steenblik et al;    -   U.S. Pat. No. 7,221,845 entitled “Planar optical waveguide”        issued May 22, 2007 to Steenblik et al;    -   U.S. Pat. No. 7,276,770 entitled “Fast Si diodes and arrays with        high quantum efficiency built on dielectrically isolated wafers”        issued Oct. 2, 2007 to Goushcha et al;    -   U.S. Pat. No. 7,530,693 entitled “Single MEMS imager optical        engine” issued May 12, 2009 to Mihalakis;    -   U.S. Pat. Pub. No. 2002/0137227 entitled “Chemiluminescent gas        analyzer” published Sep. 26, 2002 in the name of Weckstrom;    -   U.S. Pat. Pub. No. 2004/0151460 entitled “Deep trenches for        optical and electrical isolation” published Aug. 5, 2004 in the        names of Kitcher et al;    -   U.S. Pat. Pub. No. 2005/0105842 entitled “Integrated optical        arrangement” published May 19, 2005 in the names of Vonsovici et        al;    -   U.S. Pat. Pub. No. 2008/0019652 entitled “Planar optical        waveguide” published Jan. 24, 2008 in the names of Steenblik et        al; and    -   U.S. Pat. Pub. No. 2009/0080084 entitled “Beam dump for a        very-high-intensity laser beam” published Mar. 26, 2009 in the        names of Pang et al.

FIGS. 2A and 2B illustrate schematically a waveguide tap and alight-trapping structure (i.e., one or more light collectors and one ormore light traps) formed on a waveguide substrate or optical waveguidelayers thereon. FIGS. 3A/3B, 4A/4B, 5A/5B, 6A/6B, 7A/7B, and 8A/8B areschematic sectional views of various waveguide layer lateral surfaces orend faces.

Without any light-trapping structure, a stray optical signal 38 emergingfrom waveguide 46 can propagate through the optical waveguide layers 20and can in some instances interfere with or disrupt the performance ofother optical components of the optoelectronic device on the substrate20, e.g., if the arrangements of FIG. 1A or 1B do not reducesufficiently the level of the stray optical signal 38. FIGS. 2A and 2Billustrate schematically a light-trapping structure that includes lightcollectors 110 a/110 b (referred to generically as light collector 110 xor collectively as light collectors 110) and a light trap 120, althoughthe distinction between the light collectors 110 and light trap 120 issomewhat artificial in some arrangements. Two light collectors 110 andone light trap 120 are shown in the exemplary embodiment of thedrawings; any suitable number of one or more light collectors or one ormore light traps can be employed within the scope of the presentdisclosure or appended claims. Each light collector 110 x comprises oneor more lateral surfaces 112 of the optical waveguide layers 20 and asubstantially opaque coating 130 on the lateral surfaces 112 (FIGS.3A/4A/5A, which show the lateral surfaces 112 near various types ofwaveguide cores). Each light trap 120 comprises one or more lateralsurfaces 122 of the optical waveguide layers 20 and a substantiallyopaque coating 130 on the lateral surfaces 122 (FIGS. 3B/4B/5B, whichshow various core layers or cladding layers near lateral surface 112,but no waveguide core nearby). The lateral surfaces 112/122 typicallyare substantially perpendicular to the substrate 10 and opticalwaveguide layers 20, i.e., they are substantially vertical relative tothe horizontal substrate 10. The designations horizontal and verticalare relative and are not intended to designate absolute spatialorientation. Although FIGS. 3A/4A/5A show the lateral surface 112 formednear a waveguide 44 (as is the case for light collector 110 b, forexample), a light collector 110 x can be formed in any suitable locationon substrate 10, including locations away from any waveguide (whichwould therefore resemble FIGS. 3B/4B/5B). Likewise, although FIGS.3B/4B/5B show the lateral surface 122 formed away from any waveguidecore, a light trap 120 can be formed in any suitable location onsubstrate 10, including locations near a waveguide 40, 44, or 46 (whichwould therefore resemble FIGS. 3A/4A/5A).

The dumped secondary optical signal 36 propagates to the end of thesecondary waveguide 46, enters the waveguide layers 20, and propagatesaway from the end face of secondary waveguide 46 within the opticalwaveguide layers 20 as stray optical signal 38. In the example of FIGS.2A and 2B, the lateral surface 112 of light collector 110 a forms theend face of secondary waveguide 46 (similar to FIG. 1B). When the strayoptical signal 38 encounters a lateral surface 112 with a substantiallyopaque coating 130, it is prevented from propagating further in thatdirection. The coating 130 typically absorbs a fraction of the incidentlight and reflects the rest, which propagates as the stray opticalsignal 38. The lateral surface 112 of the light collector 110 a isarranged to direct the reflected portion of the stray optical signaltoward the light trap 120 (either directly, as shown, or afterredirection by another light collector 110 x, not shown).

The core of the secondary waveguide 46 can extend all the way to the endface formed by lateral surface 112 of light collector 110 a, as shownschematically in the longitudinal sections of FIGS. 6A/7A/8A (which showvarious types of waveguides terminating at surface 112). The strayoptical signal 38 emerging from the secondary waveguide 46 isimmediately reflected by surface 112 and coating 130 and propagateswithin core layers 20 without lateral confinement by a waveguide.Alternatively, the core of secondary waveguide 46 can stop short of thelateral surface 112 of the light collector 110 a, as shown schematicallyin the longitudinal sections of FIGS. 6B/7B/8B (which show various typesof waveguides terminating near surface 112). In that arrangement thestray optical signal 38 begins to diverge within the waveguide layers 20before being blocked and reflected by surface 112 and coating 130. Inany of these examples, any end face of secondary waveguide 46 isoriented off-normal from the propagation direction defined by thesecondary waveguide, so as to substantially avoid retroreflection of aportion of the secondary optical signal backward to propagate alongsecondary waveguide 46 as a guided optical mode.

The lateral surfaces 122 and substantially opaque coatings 130 of thelight trap 120 define a corresponding spiral region of the opticalwaveguide layers 20. That spiral region includes an open mouth 124 and aclosed end 126. Portions of the stray optical signal 38 that propagatein the optical waveguide layers 20 into the open mouth 124 arerepeatedly reflected from the surface 122 and coating 130 further intothe spiral region until reaching the closed end 126 (as shown in FIG.2B). Typically, upon each reflection a portion of the stray opticalsignal 34 is absorbed and the rest is reflected. The spiral region canbe arranged in any suitable way, and typically subtends an arc greaterthan about 180°. In some embodiments, the spiral region can be acornuate spiral region (i.e., a tapered, horn-shaped spiral that taperstoward the closed end 126).

The substantially opaque coating 130 typically is arranged to exhibitoptical absorption over the operational wavelength range of the lightsource 90, to effect attenuation of the stray optical signal 38 as it isrepeatedly reflected from lateral surfaces 112/122. A metal coating canoften be employed to provide substantial opacity and a suitable degreeof optical absorption. In one example, chromium or titanium can beemployed over an operational wavelength range of about 1200-1700 nm; anyother suitable metal usable over any other suitable wavelength rangeshall fall within the scope of the present disclosure or appendedclaims. A thickness of coating 130 greater than about 150 nm cantypically provide a sufficient degree of opacity, and larger thicknessescan be employed to ensure adequate opacity. In one example, wherein achromium or titanium layer is deposited on the lateral surfaces 112/122of optical waveguide layers 20 that comprise, e.g., silica, siliconnitride, or other dielectric materials of similar refractive index,about 45% of the incident stray optical signal 38 is absorbed and about55% of the stray optical signal 38 is reflected. Each ray representingthe stray optical signal 38 undergoes 4 to 6 or more reflection beforereaching the closed end 126 of the light trap 120, so that only about 3%(after 6 reflections) to about 9% (after 4 reflections) of the originaloptical power remains in the stray optical signal 38 upon reaching theclosed end 126 of the light trap 120. At that low level the strayoptical signal 38 is less likely to interfere with or disrupt operationof other optical devices on the substrate. If upon additionalreflections a portion of the stray optical signal 38 reemerges from thelight trap through its open mouth 124, it typically would be attenuatedto a substantially negligible level (e.g., less than about 1% or evenless than about 0.1%). In the examples shown, light collector 110 bintercepts some of those portions of the stray optical signal 38 thatreemerge from the light trap 120, and other such reemergent portions areintercepted by light collector 110 a.

Other suitable arrangements of one or more light collectors or lighttraps can be employed. In one particularly simple example (not shown),the secondary waveguide 46 terminates at a transmissive end face so thatthe stray optical signal 38 emergent from the waveguide 46 propagateswithin the waveguide layers 20 directly into the open mouth 124 of alight trap 120, without being redirected by reflection from any surface112. In other examples (not shown), one or more light collectors 110 orlight traps 120 can be employed in the arrangements of FIG. 1A or 1B tocontain portions of the dumped optical signal 36 or stray optical signal38 that might be internally reflected by the edge of the waveguidelayers 20.

In some instances the amount of optical signal power reaching the endface of secondary waveguide 46 (at the surface 112 of the lightcollector 110 a as in FIG. 1B, 2A, or 2B) can be sufficient to perturboperation of the optoelectronic device (e.g., by localized heating dueto optical absorption), or to cause damage to the surface 112, coating130, or waveguide layers 20. In such an instance, the opaque coating 130on the end face of the waveguide 46 can be chosen to be relativelyhigher reflecting than those described above, e.g., coating 130 cancomprise gold, silver, or other highly reflective, relativelynon-absorptive metal on the end face of secondary waveguide 46. Thestray optical signal 38 would not be absorbed to a significant extent atthe end face of waveguide 46 by such a coating. The first time opticalsignal 38 would encounter a partially absorptive coating 130 (e.g.,within trap 120 in the exemplary arrangement of FIGS. 2A and 2B), itwould have diverged to a significant extent due to unconfinedpropagation within waveguide layers 20. The resulting decrease in powerdensity would reduce or eliminate problems arising from localizedheating or optical damage.

A reflection suppressing layer (i.e., anti-reflection coating) can beemployed as a portion of coating 130, between the lateral surface112/122 and the metal absorbing layer. Reduction of the amount of lightreflected (and concomitant increase in the amount absorbed) upon eachencounter with a surface 112/122 enhances the attenuation of the strayoptical signal 34 as it repeatedly encounters surfaces 112/122. Anysuitable reflection suppression layer or anti-reflection coating can beemployed. Some examples are disclosed in co-owned U.S. Pat. No.7,943,229, which is hereby incorporated by reference as if fully setforth herein.

The lateral surfaces 112/122 in the examples of FIGS. 3A/3B, 4A/4B, and5A/5B, and the end faces in the examples of 6A/6B, 7A/7B, and 8A/8B, areshown extending through the entirety of the optical waveguide layers 20but not extending into the waveguide substrate 10. Other suitable depthscan be employed within the scope of the present disclosure or appendedclaims, however, it is typically preferable for the lateral surface112/122 to extend at least through the entirety of the optical waveguidelayers 20. The lateral surfaces 112/122 can extend into the waveguidesubstrate 10. It may often occur that the optical waveguide layers 20,waveguides 40/44/46, tap 42, surfaces 112/122, and coatings 130 areformed or deposited on a wafer scale to fabricate light collectors andtraps on many waveguide substrates simultaneously. The lateral surfaces112/122 can be formed during such wafer-scale fabrication, e.g., by anysuitable dry or wet etch process, typically by etching one or moretrenches into the optical waveguide layers 20 (and perhaps extendinginto the substrate 10, as noted above).

As shown in the exemplary arrangements of FIG. 3A/3B, 4A/4B, 5A/5B,6A/6B, 7A/7B, or 8A/8B, differing arrangements for the layer 130 can beemployed. In the arrangement of FIGS. 3A/3B, the coating 130 overliesonly the lateral surface 112/122; in the arrangement of FIGS. 6A/6B, thecoating 130 overlies only the end face of secondary waveguide 46.Practically, that may be all that is needed, but also practically, thatarrangement can be difficult to achieve, particularly using standardlithographic deposition techniques to form light collectors and traps onmany waveguide substrates simultaneously. Conformal (i.e.,non-directional) deposition techniques are not well-suited for selectivecoverage of only surfaces of a particular orientation, and directionaldeposition techniques are not well-suited for selective coverage of onlyvertical surfaces. The arrangement of FIG. 4A/4B or 7A/7B can be theeasiest to achieve, by simply coating all, or nearly all, of the exposedsurfaces of the waveguide substrate 10 and optical waveguide layers 20.That approach can be employed if there is no reason to avoid thepresence of coating 130 over the waveguides 40 or 44 or over otherportions of the waveguide substrate 10 or optical waveguide layers 20,and if a deposition can be employed that is at least somewhat conformal.An intermediate approach is illustrated by the exemplary arrangementshown in FIG. 5A/5B or 8A/8B, in which the coating 130 extends partlyacross horizontal surfaces of waveguide substrate 10 or opticalwaveguide layers 20. Portions of the substrate 10 or waveguide layers 20can be masked to prevent deposition of the coating 130 onto areas whereit would be undesirable.

Differing arrangements of the optical waveguide 44 and the opticalwaveguide layers 20 are shown in the exemplary arrangements of FIG.3A/3B, 4A/4B, or 5A/5B; differing arrangements of the optical waveguide46 and the optical waveguide layers 20 are shown in the exemplaryarrangements of FIG. 6A/6B, 7A/7B, or 8A/8B. Any of the waveguidearrangements in those examples can be employed in any combination withany of the arrangements shown for coating 130 in those examples. In theexamples shown in FIG. 3A/3B or 6A/6B, the optical waveguide 44 or 46comprises a single, higher-index core between top and bottom lower-indexcladding layers. A lateral surface 112 is shown near the waveguide 44 inFIG. 3A, while only the two cladding layers are present near the lateralsurface 122 shown in FIG. 3B. The waveguide core and cladding layers areshown extending to the end face of waveguide 46 in FIG. 6A, but only thecladding layers reach the end face in FIG. 6B.

In the examples shown in FIG. 4A/4B or 7A/7B, the optical waveguide 44or 46 comprises a pair of higher-index cores and top, middle, and bottomlower-index cladding layers. A lateral surface 112 is shown near thewaveguide 44 in FIG. 4A, while only the three cladding layers arepresent near the lateral surface 122 shown in FIG. 4B. The waveguidecore and cladding layers are shown extending to the end face ofwaveguide 46 in FIG. 7A, but only the cladding layers reach the end facein FIG. 7B. In the examples shown in FIG. 5A/5B or 8A/8B, the opticalwaveguide 44 or 46 comprises one higher-index core and two higher-indexcore layers, and the cladding comprises top, upper middle, lower middle,and bottom lower-index cladding layers. A lateral surface 112 is shownnear the waveguide 44 in FIG. 5A, while the four cladding layers and thetwo core layers (without the core) are present near the surface lateral122 shown in FIG. 5B. The waveguide core, core layers, and claddinglayers are shown extending to the end face of waveguide 46 in FIG. 8A,but only the cladding layers and the two core layers (but not the core)reach the end face in FIG. 8B. Boundaries are shown between the variouscladding layers to indicate where cladding deposition is interrupted toallow deposition or patterning of an intervening core or core layer,however, such boundaries may or may not be readily apparent in thefinished device, particularly if the same material is used for thedifferent cladding layers.

In addition to coating 130 on a lateral surface 112 or 122, it can beadvantageous to employ an optically absorbing encapsulant (e.g., carbonparticles dispersed in a silicone, epoxy, or polyurethane polymer) thatsubstantially covers the lateral surface 112 or 122 of a light collector110 or light trap 120. Such encapsulation (which can also serve as theindex matching or absorptive medium described in connection with thearrangements of FIGS. 1A and 1B) can attenuate portions of the strayoptical signal 38 that might leak through or be scattered from coating130, thereby enhancing the performance of the light collector 110 orlight trap 120 (if such enhancement is needed or desired). In oneexample, use of light collectors and light traps combined with use of anoptically absorbing encapsulant can reduce optical cross-talk in abidirectional optoelectronic device to a greater degree than the lightcollectors and trap without such encapsulation. Any suitable opticallyabsorbing encapsulant can be employed. Some examples of suitableencapsulants are disclosed in some of the co-owned applicationsincorporated above; some of those examples include dual-functionencapsulation that can also reduce electrical cross-talk in anoptoelectronic device (if needed or desired).

In the exemplary embodiments of FIGS. 1B, 2A, and 2B, a first lightcollector 110 a is substantially flat (in the case of FIGS. 2A and 2B,so as to redirect the stray optical signal 38 toward the open mouth oflight trap 120 without substantially altering its divergencecharacteristics). A second light collector 110 b in FIGS. 2A and 2B iscurved so as to alter the divergence of a portion of the stray opticalsignal 38 that reemerges from the light trap 120. The illustrated shapesand arrangements of light collectors 110 a and 110 b are only exemplary;other shapes or arrangements of curved or straight light collectorsurfaces 112 can be employed as needed or desired.

To further reduce the likelihood of the stray optical signal 38disrupting the operation of the optoelectronic device, the waveguide 44can include a curved segment that routes the primary optical signal 34to regions of the waveguide substrate 10 and waveguide layers 20 thatare obstructed by the light collectors 110 or the light trap 120; Suchan arrangement is shown in various of the drawings. Components of theoptoelectronic device that the stray optical signal 38 could disturb canbe positioned on such obstructed regions of the substrate 10 orwaveguide layers 20. However, a curved waveguide arrangement is notalways necessary or desirable; any suitable arrangement or routing ofwaveguides on the substrate 10 can be employed within the scope of thepresent disclosure or appended claims.

In some cases, a waveguide tap 42 employed to reduce the power of theoptical signal 30 exhibits a wavelength-dependent division of opticalpower between optical signals 34 and 36. If the wavelength of theoptical signal 30 varies, the wavelength variation of the waveguide tap42 results in power fluctuations in optical signal 34. In some instancessuch power fluctuations might be operationally acceptable and might notunduly degrade performance of the optoelectronic device. In otherinstances such power fluctuations are not acceptable. In anoptoelectronic device that includes a power monitor (e.g., a monitorphotodiode) and electronic feedback control of the light source, theoptical signal 34 can be monitored downstream of the waveguide tap 42(as in the exemplary arrangement of FIG. 9B). In that way, theelectronic feedback control can compensate for power fluctuationsarising from the wavelength dependence of the waveguide tap 42. However,in some instances adequate feedback control can be achieved bymonitoring the optical signal 30 upstream of the waveguide tap 42 (as inthe exemplary arrangement of FIG. 9A).

One difficulty that can arise in power monitoring and electronicfeedback control of the light source is that the monitor signal powercan depend on wavelength (commonly referred to as “tracking error”);such a wavelength dependence typically arises from wavelength dependenceof an optical waveguide tap used to obtain the monitor optical signal.If the optical signal power levels required for laser monitoring and fortransmission by the optoelectronic device are similar, then theexemplary arrangement of FIG. 9A can be employed and adapted tocompensate for the wavelength dependence. To compensate for trackingerror, the waveguide taps 42 and 43 can be arranged nominallyidentically in terms of core sizes, spacings, and materials, so thatboth waveguide taps exhibit the same tap ratio and wavelength dependencethereof. This of course assumes that a common tap ratio can be employedthat provides a suitable optical power level for both optical signals 34and 35. The tap 43 splits off a monitor optical signal 35 thatpropagates along waveguide 45 to a monitor photodetector (not shown).The tap 42 splits off a substantially identical fraction of the powerremaining in the optical signal 30 to propagate as primary opticalsignal 34 along waveguide 44. Because the tap 42 and 43 aresubstantially identical, any wavelength dependence of the tap ratioswill cancel out and the power in optical signals 34 and 35 willprecisely track one another. Electronic feedback control using signal 35results in substantially identical control of signal 34 (i.e., theoutput signal of the optoelectronic device). This particular “balanced”arrangement of the example of FIG. 9A does not depend on the placementorder of the taps 42 and 43 along the waveguides 40 or 46.

The arrangement of FIG. 9B can also mitigate the effects of wavelengthdependence of waveguide taps 42. Once again, if optical signal powerlevels for monitoring and transmission are similar, then tap 42 can bearranged to split about twice the desired fraction of optical signal 30to propagate as primary signal 34 along waveguide 44. A substantiallysymmetric monitor tap or splitter 43 can be employed to evenly dividethe optical signal 34: one portion propagates as monitor signal 35 alongwaveguide 45 to the monitor photodetector (not shown), and the secondportion continues along waveguide 44 as primary optical signal 34.Again, this assumes that a common tap ratio can be employed thatprovides a suitable optical power level for both optical signals 34 and35. Because splitter 43 is symmetric, it will not exhibit substantialwavelength dependence of its tap ratio, and again the optical signals 34and 35 will precisely track one another.

In addition to the preceding, the following examples fall within thescope of the present disclosure or appended claims:

Example 1

An optical apparatus comprising: a waveguide substrate; a set of one ormore optical waveguide layers on the substrate; source, primary, andsecondary optical waveguides formed in one or more of the opticalwaveguide layers, each of the optical waveguides being arranged tosubstantially confine in two transverse dimensions a correspondingguided optical mode; a light source that emits an optical signal and isarranged to launch a portion of the optical signal to propagate alongthe source waveguide as a source optical signal in the correspondingguided optical mode; and a first optical waveguide tap formed in one ormore of the optical waveguide layers and arranged to direct a primaryfraction of the source optical signal to propagate along the primarywaveguide as a primary optical signal and to direct a secondary fractionof the source optical signal to propagate along the secondary waveguideas a secondary optical signal, wherein the secondary waveguide isarranged so that the secondary optical signal propagates to an end ofthe secondary waveguide, propagates to an edge of the waveguidesubstrate, and emerges from the optical waveguide layers.

Example 2

The apparatus of Example 1 further comprising a light collector formedin the optical waveguide layers and comprising one or more lateralsurfaces of the optical waveguide layers and a substantially opaquecoating on the lateral surfaces, wherein the lateral surfaces of thelight collector are arranged on the waveguide substrate to redirect thesecondary optical signal emergent from the secondary waveguide topropagate to the edge of the waveguide substrate without confinement byany of the optical waveguides in the corresponding guided optical modes.

Example 3

The apparatus of Example 1 further comprising one or more light trapsformed in the optical waveguide layers, each light trap comprising oneor more lateral surfaces of the optical waveguide layers and asubstantially opaque coating on the lateral surfaces, wherein: thelateral surfaces of each light trap are arranged to define acorresponding spiral region of the optical waveguide layers, whichregion includes an open mouth and closed end of the light trap; and thesecondary waveguide and the light trap are arranged on the waveguidesubstrate so that a stray optical signal reflected from an edge of theoptical waveguide layers at the edge of the waveguide substratepropagates into the open mouth of the optical trap without confinementby any of the optical waveguides in the corresponding guided opticalmodes.

Example 4

An optical apparatus comprising: a waveguide substrate; a set of one ormore optical waveguide layers on the substrate; source, primary, andsecondary optical waveguides formed in one or more of the opticalwaveguide layers, each of the optical waveguides being arranged tosubstantially confine in two transverse dimensions a correspondingguided optical mode; a light source that emits an optical signal and isarranged to launch a portion of the optical signal to propagate alongthe source waveguide as a source optical signal in the correspondingguided optical mode; a first optical waveguide tap formed in one or moreof the optical waveguide layers and arranged to direct a primaryfraction of the source optical signal to propagate along the primarywaveguide as a primary optical signal and to direct a secondary fractionof the source optical signal to propagate along the secondary waveguideas a secondary optical signal; and one or more light traps formed in theoptical waveguide layers, each light trap comprising one or more lateralsurfaces of the optical waveguide layers and a substantially opaquecoating on the lateral surfaces, wherein: the lateral surfaces of eachlight trap are arranged to define a corresponding spiral region of theoptical waveguide layers, which region includes an open mouth and closedend of the light trap; the secondary waveguide is arranged so that thesecondary optical signal propagates to an end of the secondary waveguideand emerges from the secondary waveguide to propagate as a stray opticalsignal in one or more of the optical waveguide layers withoutconfinement by any of the optical waveguides in the corresponding guidedoptical modes; and the secondary waveguide and the light trap arearranged on the waveguide substrate so that the stray optical signalpropagates into the open mouth of the optical trap without confinementby any of the optical waveguides in the corresponding guided opticalmodes.

Example 5

The apparatus of Example 4 further comprising one or more lightcollectors formed in the optical waveguide layers, each light collectorcomprising one or more lateral surfaces of the optical waveguide layersand a substantially opaque coating on the lateral surfaces, wherein thelateral surfaces of each light collector are arranged on the waveguidesubstrate to redirect a corresponding portion of the stray opticalsignal to propagate into the open mouth of one of the light trapswithout confinement by any of the optical waveguides in thecorresponding guided optical modes.

Example 6

The apparatus of any one of Examples 2 or 5 wherein one of the lightcollectors is arranged on the waveguide substrate so that one of itslateral surfaces forms an at least partly reflective end face of thesecondary waveguide.

Example 7

The apparatus of Example 5 wherein at least one of the light collectorsis arranged on the waveguide substrate to redirect at least a portion ofthe stray optical signal emerging from the mouth of the light trap topropagate back into the mouth of the light trap.

Example 8

The apparatus of any preceding Example wherein the substrate comprisessilicon or doped silicon, and one or more of the optical waveguidelayers comprises silica, doped silica, silicon nitride, or siliconoxynitride.

Example 9

The apparatus of any preceding Example wherein one or more of theoptical waveguide layers comprises one or more inorganic, doped orundoped, dielectric core or cladding materials.

Example 10

The apparatus of any preceding Example wherein one or more of theoptical waveguide layers comprises one or more polymer or organic, dopedor undoped, dielectric core or cladding materials.

Example 11

The apparatus of any preceding Example wherein the one or more opticalwaveguide layers include one or more doped or undoped inorganicsemiconductor core materials and one or more doped or undoped inorganicdielectric cladding materials.

Example 12

The apparatus of any preceding Example wherein the one or more opticalwaveguide layers include one or more doped or undoped polymer or organicsemiconductor core materials and one or more doped or undoped polymer ororganic dielectric cladding materials.

Example 13

The apparatus of any preceding Example wherein the light sourcecomprises a laser diode or a light emitting diode.

Example 14

The apparatus of any preceding Example wherein the light source ispositioned on the substrate or on one or more of the waveguide layers.

Example 15

The apparatus of any one of Examples 2 through 14 wherein one or more ofthe lateral surfaces of the light collectors or the light traps compriseetched edges of one or more of the optical waveguide layers.

Example 16

The apparatus of any one of Examples 2 through 15 wherein thesubstantially opaque coatings of one or more of the lateral surfaces ofthe light collectors or light traps include a metal layer.

Example 17

The apparatus of Example 16 wherein the metal layer is at least partlyabsorptive.

Example 18

The apparatus of any one of Examples 16 or 17 wherein the metal layer isat least partly reflective.

Example 19

The apparatus of claim 16 wherein the metal layer is at least partlyabsorptive, and the substantially opaque coating includes a reflectionsuppressing layer between the lateral surface and the metal layer.

Example 20

The apparatus of any one of Examples 3 through 19 wherein the spiralregion subtends an arc greater than about 180°.

Example 21

The apparatus of any one of Examples 3 through 20 wherein at least aportion of the spiral region is a cornuate spiral region.

Example 22

The apparatus of any preceding Example further comprising an opticallyabsorptive encapsulant that substantially covers (i) one or more edgesof the waveguide layers at the edge of the waveguide substrate or (ii)one or more of the lateral surfaces of one or more of the light traps orlight collectors.

Example 23

The apparatus of Example 22 wherein the encapsulant comprises asilicone, epoxy, or polyurethane polymer.

Example 24

The apparatus of Example 23 wherein the encapsulant further comprisescarbon particles dispersed in the polymer.

Example 25

The apparatus of any preceding Example further comprising a secondoptical waveguide tap arranged to direct a monitor fraction of (i) theoptical signal propagating along the source waveguide, or (ii) thesecondary optical signal propagating along the secondary waveguide, topropagate along a monitor optical waveguide to a monitor photodetector.

Example 26

The apparatus of Example 25 wherein the second optical waveguide tap issubstantially identical to the first optical waveguide tap.

Example 27

The apparatus of any one of Examples 1 through 24 further comprising asecond optical waveguide tap, wherein the second optical waveguide tapis substantially symmetric and is arranged to divide the primary opticalsignal into substantially equal first and second fractions thatpropagate (i) along the monitor optical waveguide to a monitorphotodetector and (ii) along an extension of the primary waveguidebeyond the second optical waveguide tap, respectively.

Example 28

A method for making the optical apparatus of any preceding Example, themethod comprising: forming source, primary, and secondary opticalwaveguides in one or more of a set of optical waveguide layers formed ona waveguide substrate; arranging a light source to launch a sourceoptical signal to propagate along the source waveguide in thecorresponding guided optical mode; and forming an optical waveguide tapin one or more of the optical waveguide layers and arranging the tap todirect a primary fraction of the source optical signal to propagatealong the primary waveguide as a primary optical signal and to direct asecondary fraction of the source optical signal to propagate along thesecondary waveguide as a primary optical signal, and further comprising:arranging the secondary waveguide so that the secondary optical signalpropagates to an end of the secondary waveguide, propagates to an edgeof the waveguide substrate, and emerges from the optical waveguidelayers; or forming one or more light traps in the optical waveguidelayers, each light trap comprising one or more lateral surfaces of theoptical waveguide layers and a substantially opaque coating on thelateral surfaces.

Example 29

A method for using the apparatus of any preceding Example comprisingoperating the light source to launch the source optical signal topropagate along the source waveguide in the corresponding guided opticalmode.

It is intended that equivalents of the disclosed exemplary embodimentsand methods shall fall within the scope of the present disclosure orappended claims. It is intended that the disclosed exemplary embodimentsand methods, and equivalents thereof, may be modified while remainingwithin the scope of the present disclosure or appended claims.

In the foregoing Detailed Description, various features may be groupedtogether in several exemplary embodiments for the purpose ofstreamlining the disclosure. This method of disclosure is not to beinterpreted as reflecting an intention that any claimed embodimentrequires more features than are expressly recited in the correspondingclaim. Rather, as the appended claims reflect, inventive subject mattermay lie in less than all features of a single disclosed exemplaryembodiment. Thus, the appended claims are hereby incorporated into theDetailed Description, with each claim standing on its own as a separatedisclosed embodiment. However, the present disclosure shall also beconstrued as implicitly disclosing any embodiment having any suitableset of one or more disclosed or claimed features (i.e., sets of featuresthat are not incompatible or mutually exclusive), including those setsthat may not be explicitly disclosed herein. It should be further notedthat the scope of the appended claims do not necessarily encompass thewhole of the subject matter disclosed herein.

For purposes of the present disclosure and appended claims, theconjunction “or” is to be construed inclusively (e.g., “a dog or a cat”would be interpreted as “a dog, or a cat, or both”; e.g., “a dog, a cat,or a mouse” would be interpreted as “a dog, or a cat, or a mouse, or anytwo, or all three”), unless: (i) it is explicitly stated otherwise,e.g., by use of “either . . . or,” “only one of,” or similar language;or (ii) two or more of the listed alternatives are mutually exclusivewithin the particular context, in which case “or” would encompass onlythose combinations involving non-mutually-exclusive alternatives. Forpurposes of the present disclosure or appended claims, the words“comprising,” “including,” “having,” and variants thereof, wherever theyappear, shall be construed as open ended terminology, with the samemeaning as if the phrase “at least” were appended after each instancethereof.

In the appended claims, if the provisions of 35 USC §112 ¶6 are desiredto be invoked in an apparatus claim, then the word “means” will appearin that apparatus claim. If those provisions are desired to be invokedin a method claim, the words “a step for” will appear in that methodclaim. Conversely, if the words “means” or “a step for” do not appear ina claim, then the provisions of 35 USC §112 ¶6 are not intended to beinvoked for that claim.

The Abstract is provided as required as an aid to those searching forspecific subject matter within the patent literature. However, theAbstract is not intended to imply that any elements, features, orlimitations recited therein are necessarily encompassed by anyparticular claim. The scope of subject matter encompassed by each claimshall be determined by the recitation of only that claim.

1. (canceled)
 2. (canceled)
 3. The apparatus of claim 22 wherein one ofthe light collectors is arranged on the waveguide substrate so that onelateral surface thereof forms an at least partly reflective end face ofthe secondary waveguide.
 4. (canceled)
 5. The apparatus of claim 21wherein the light source is positioned on the substrate or on one ormore of the waveguide layers.
 6. The apparatus of claim 22 wherein oneor more of the lateral surfaces of the one or more light collectorscomprise etched edges of one or more of the optical waveguide layers. 7.The apparatus of claim 22 wherein the substantially opaque coatings ofone or more of the lateral surfaces of the one or more light trapsinclude a metal layer.
 8. The apparatus of claim 7 wherein the metallayer is at least partly absorptive.
 9. The apparatus of claim 7 whereinthe metal layer is at least partly reflective.
 10. The apparatus ofclaim 7 wherein the metal layer is at least partly absorptive, and thesubstantially opaque coating includes a reflection suppressing layerbetween the lateral surface and the metal layer.
 11. (canceled) 12.(canceled)
 13. The apparatus of claim 21 further comprising an opticallyabsorptive encapsulant that substantially covers one or more edges ofthe waveguide layers at the edge of the waveguide substrate. 14.(canceled)
 15. (canceled)
 16. The apparatus of claim 21 furthercomprising a second optical waveguide tap arranged to direct a monitorfraction of (i) the optical signal propagating along the sourcewaveguide, or (ii) the secondary optical signal propagating along thesecondary waveguide, to propagate along a monitor optical waveguide to amonitor photodetector.
 17. The apparatus of claim 16 wherein the secondoptical waveguide tap is substantially identical to the first opticalwaveguide tap.
 18. The apparatus of claim 21 further comprising a secondoptical waveguide tap, wherein the second optical waveguide tap issubstantially symmetric and is arranged to divide the primary opticalsignal into substantially equal first and second fractions thatpropagate (i) along a monitor optical waveguide to a monitorphotodetector and (ii) along an extension of the primary waveguidebeyond the second optical waveguide tap, respectively.
 19. (canceled)20. (canceled)
 21. An optical apparatus comprising: a waveguidesubstrate; one or more optical waveguide layers on the substrate;source, primary, and secondary optical waveguides formed in one or moreof the optical waveguide layers, each of the optical waveguides beingarranged to substantially confine in two transverse dimensions acorresponding guided optical mode; a light source that emits an opticalsignal and is arranged to launch a portion of the optical signal topropagate along the source waveguide as a source optical signal in thecorresponding guided optical mode; and a first optical waveguide tapformed in one or more of the optical waveguide layers and arranged todirect a primary fraction of the source optical signal to propagatealong the primary waveguide as a primary optical signal and to direct asecondary fraction of the source optical signal to propagate along thesecondary waveguide as a secondary optical signal, wherein the secondarywaveguide is arranged so that the secondary optical signal propagates toan end of the secondary waveguide and emerges from transmissive lateralsurfaces of the optical waveguide layers at the edge of the waveguidesubstrate.
 22. The apparatus of claim 21 further comprising one or morelight collectors formed in the optical waveguide layers and comprisingone or more lateral surfaces of the optical waveguide layers and asubstantially opaque coating on the lateral surfaces, wherein thelateral surfaces of the one or more light collectors are arranged on thewaveguide substrate to redirect the secondary optical signal emergentfrom the secondary waveguide to propagate within the optical waveguidelayers to the edge of the waveguide substrate without confinement by anyof the optical waveguides in the corresponding guided optical modes. 23.(canceled)
 24. A method for making an optical apparatus, the methodcomprising: forming source, primary, and secondary optical waveguides inone or more optical waveguide layers formed on a waveguide substrate;arranging a light source to launch a source optical signal to propagatealong the source waveguide in the corresponding guided optical mode; andforming an optical waveguide tap in one or more of the optical waveguidelayers and arranging the tap to direct a primary fraction of the sourceoptical signal to propagate along the primary waveguide as a primaryoptical signal and to direct a secondary fraction of the source opticalsignal to propagate along the secondary waveguide as a secondary opticalsignal, wherein the secondary waveguide is arranged so that thesecondary optical signal propagates to an end of the secondary waveguideand emerges from transmissive lateral surfaces of the optical waveguidelayers at the edge of the waveguide substrate.
 25. The method of claim24 further comprising forming one or more light collectors in theoptical waveguide layers, the one or more light collectors comprisingone or more lateral surfaces of the optical waveguide layers and asubstantially opaque coating on the lateral surfaces, wherein thelateral surfaces of the one or more light collectors are arranged on thewaveguide substrate to redirect the secondary optical signal emergentfrom the secondary waveguide to propagate within the optical waveguidelayers to the edge of the waveguide substrate without confinement by anyof the optical waveguides in the corresponding guided optical modes. 26.A method for using an optical apparatus, the method comprising:operating a light source to launch a source optical signal to propagatealong a source waveguide in a corresponding guided optical mode;directing a primary fraction of the source optical signal to propagatealong a primary waveguide as a primary optical signal in a correspondingguided optical mode; directing a secondary fraction of the sourceoptical signal to propagate along and to an end of a secondary waveguideas a secondary optical signal in a corresponding guided optical mode;and discarding the secondary optical signal by directing the secondaryoptical signal to emerge from transmissive lateral surfaces of opticalwaveguide layers at an edge of a waveguide substrate, wherein theoptical apparatus comprises: the waveguide substrate; the one or moreoptical waveguide layers on the substrate; the source optical waveguide,the primary optical waveguide, and the secondary optical waveguideformed in one or more of the optical waveguide layers, each of theoptical waveguides being arranged to substantially confine in twotransverse dimensions a corresponding guided optical mode; the lightsource; and a first optical waveguide tap formed in one or more of theoptical waveguide layers and arranged to direct the primary fraction ofthe source optical signal to propagate along the primary waveguide asthe primary optical signal and to direct the secondary fraction of thesource optical signal to propagate along the secondary waveguide as thesecondary optical signal.
 27. The method of claim 26 further comprisingredirecting, with one or more light collectors formed in the opticalwaveguide layers, the secondary optical signal emergent from thesecondary waveguide to propagate within the optical waveguide layers tothe edge of the waveguide substrate without confinement by any of theoptical waveguides in the corresponding guided optical modes, whereinthe one or more light collectors comprise one or more lateral surfacesof the optical waveguide layers and a substantially opaque coating onthe lateral surfaces.